The effect of cytokines on the replication of T. gondii within rat retinal vascular endothelial cells

Toxoplasma gondii activates a Syk-CARD9-NF-κB signaling axis and gasdermin D-independent release of IL-1β during infection of primary human monocytes

IL-1β is a potent pro-inflammatory cytokine that promotes immunity and host defense, and its dysregulation is associated with immune pathology. Toxoplasma gondii infection of myeloid cells triggers the production and release of IL-1β; however, the mechanisms regulating this pathway, particularly in human immune cells, are incompletely understood. We have identified a novel pathway of T. gondii induction of IL-1β via a Syk-CARD9-NF-κB signaling axis in primary human peripheral blood monocytes. Syk was rapidly phosphorylated during T. gondii infection of primary monocytes, and inhibiting Syk with the pharmacological inhibitors R406 or entospletinib, or genetic ablation of Syk in THP-1 cells, reduced IL-1β release. Inhibition of Syk in primary cells or deletion of Syk in THP-1 cells decreased parasite-induced IL-1β transcripts and the production of pro-IL-1β. Furthermore, inhibition of PKCδ, CARD9/MALT-1 and IKK reduced p65 phosphorylation and pro-IL-1β production in T. gondii-infected primary monocytes, and genetic knockout of PKCδ or CARD9 in THP-1 cells also reduced pro-IL-1β protein levels and IL-1β release during T. gondii infection, indicating that Syk functions upstream of this NF-κB-dependent signaling pathway for IL-1β transcriptional activation. IL-1β release from T. gondii-infected primary human monocytes required the NLRP3-caspase-1 inflammasome, but interestingly, was independent of gasdermin D (GSDMD) cleavage and pyroptosis. Moreover, GSDMD knockout THP-1 cells released comparable amounts of IL-1β to wild-type THP-1 cells after T. gondii infection. Taken together, our data indicate that T. gondii induces a Syk-CARD9/MALT-1-NF-κB signaling pathway and activation of the NLRP3 inflammasome for the release of IL-1β in a cell death- and GSDMD-independent manner. This research expands our understanding of the molecular basis for human innate immune regulation of inflammation and host defense during parasite infection.

NLRP3 and Potassium Efflux Drive Rapid IL-1β Release from Primary Human Monocytes during Toxoplasma gondii Infection

IL-1β is produced by myeloid cells and acts as a critical mediator of host defense during infection and injury. We found that the intracellular protozoan parasite Toxoplasma gondii induced an early IL-1β response (within 4 h) in primary human peripheral blood monocytes isolated from healthy donors. This process involved upregulation of IL-1β, IL-1RN (IL-1R antagonist), and NLRP3 transcripts, de novo protein synthesis, and the release of pro- and mature IL-1β from infected primary monocytes. The released pro-IL-1β was cleavable to mature bioactive IL-1β in the extracellular space by the protease caspase-1. Treatment of primary monocytes with the NLRP3 inhibitor MCC950 or with extracellular potassium significantly reduced IL-1β cleavage and release in response to T. gondii infection, without affecting the release of TNF-α, and indicated a role for the inflammasome sensor NLRP3 and for potassium efflux in T. gondii-induced IL-1β production. Interestingly, T. gondii infection did not induce an IL-1β response in primary human macrophages derived from the same blood donors as the monocytes. Consistent with this finding, NLRP3 was downregulated during the differentiation of monocytes to macrophages and was not induced in macrophages during T. gondii infection. To our knowledge, these findings are the first to identify NLRP3 as an inflammasome sensor for T. gondii in primary human peripheral blood cells and to define an upstream regulator of its activation through the release of intracellular potassium.

T cell immunoregulation in active ocular toxoplasmosis

Toxoplasma gondii infection is an important cause of infectious ocular disease. The physiopathology of retinochoroidal lesions associated with this infection is not completely understood. The present study was undertaken to investigate cytokine production by T cells from individuals with active toxoplasmic retinochoroiditis (TR) comparing with controls. Eighteen patients with active TR and 15 healthy controls (6 controls IgG⁺ to Toxoplasma and 9 negative controls) were included in the study. Peripheral blood mononuclear cells were incubated in the presence or absence of T. gondii antigen (STAg), and stained against CD4, CD8, TNF, IL-10 and IFN-γ. Baseline expression of cytokines was higher in TR/IgG⁺ patients in comparison with controls. Cytokine expression was not increased by STAg in vitro stimulation in controls. After stimulation, TR/IgG⁺ patients' lymphocytes increased cytokine as compared to cultures from both controls. While T cells were the main source of IL-10, but also IFN-γ and TNF, other lymphocyte populations were relevant source of inflammatory cytokines. Interestingly, it was observed a negative correlation between ocular lesion size and IL-10 expression by CD4⁺ lymphocytes. This study showed that T cells are the main lymphocyte populations expressing IL-10 in patients with TR. Moreover, expression of IL-10 plays a protective role in active TR.

Toxoplasmosis

Toxoplasma gondii, an Apicomplexan, is a pathogic protozoan that can infect the central nervous system. Infection during pregnancy can result in a congenial infection with severe neurological sequelae. In immunocompromised individuals reactivation of latent neurological foci can result in encephalitis. Immunocompetent individuals infected with T. gondii are typically asymptomatic and maintain this infection for life. However, recent studies suggest that these asymptomatic infections may have effects on behavior and other physiological processes. Toxoplasma gondii infects approximately one-third of the world population, making it one of the most successful parasitic organisms. Cats and other felidae serve as the definite host producing oocysts, an environmentally resistant life cycle stage found in cat feces, which can transmit the infection when ingested orally. A wide variety of warm-blooded animals, including humans, can serve as the intermediate host in which tissue cysts (containing bradyzoites) develop. Transmission also occurs due to ingestion of the tissue cysts. There are three predominant clonal lineages, termed Types I, II and III, and an association with higher pathogenicity with the Type I strains in humans has emerged. This chapter presents a review of the biology of this infection including the life cycle, transmission, epidemiology, parasite strains, and the host immune response. The major clinical outcomes of congenital infection, chorioretinitis and encephalitis, and the possible association of infection of toxoplasmosis with neuropsychiatric disorders such as schizophrenia, are reviewed.

Toxicity of derivatives from semicarbazide-sensitive amine oxidase-mediated deamination of methylamine against Toxoplasma gondii after infection of differentiated 3T3-L1 cells

Adipose tissue plays an active role in normal metabolic homeostasis as well as in the development of human diseases such as atherosclerosis and diabetes. We report here antimicrobial activities of the metabolites from adipocytes. Specifically, semicarbazide-sensitive amine oxidase of differentiated 3T3-L1 cells was found to utilize methylamine for producing formaldehyde and hydrogen peroxide, accounting for the inhibition of infectivity of Toxoplasma gondii and its replication in these cells. This was demonstrated by the findings that semicarbazide-sensitive amine oxidase was extremely high in differentiated 3T3-L1 cells; and that the infection of these cells by T. gondii and its intracellular replication were decreased to 33% and 37% of the control, respectively, when methylamine was provided in micromolar concentrations as the substrate to the aminoxidase. Only one of the two reaction products expected was found inhibitory against T. gondii when added to the infected pre-adipocytes of 3T3-L1. Intracellular replication of this parasite was inhibited by formaldehyde in the range of 10-100 microM and stimulated by hydrogen peroxide at 1-10 microM. The finding indicates that T. gondii may be useful as a sensitive and convenient sentinel for screening agents toxic to eukaryotic cells.

Immunity and Toxoplasma retinochoroiditis

Toxoplasma infection accounts for up to 50% of all cases of posterior uveitis worldwide. In this review the control of Toxoplasma infection generally, and specific in the eye, by the immune system is discussed.

Expression analysis of immune response genes of Müller cells infected with Toxoplasma gondii

PURPOSE

To investigate changes in immune response genes following Toxoplasma gondii infection of Müller cells.

METHODS

Human Müller cells were infected or mock infected with two strains of T. gondii (RH and Prugniaud). RNA and supernatants were collected from infected and uninfected cells at 2 and 24 h. RNA from the two time points were compared using a custom made DNA microarray. Real time PCR or human cytokine antibody array was used to confirm up-regulation of immune molecules.

RESULTS

Gene expression in infected cells showed up-regulation of CCL2, IL-6, CXCL8, and CXCL2. CCL2 and CXCL2 gene expression was confirmed by real time PCR. IL-6 and CXCL8 protein production was confirmed by a cytokine antibody array. IL-4 production was observed by cytokine antibody array but not by DNA microarray. In contrast, infection with T. gondii did not induce interferon-gamma (IFNgamma) and IL-12 expression, molecules conventionally associated with the inter-conversion of tachyzoite to bradyzoite.

CONCLUSION

These results indicate that while in vitro infected Müller cells may be capable of inducing an immune response by attracting blood-borne leucocytes, they do not appear able to directly control the proliferation of T. gondii.

Toxoplasma gondii and Neospora caninum infections of bovine endothelial cells induce endothelial adhesion molecule gene transcription and subsequent PMN adhesion

Toxoplasma gondii and Neospora caninum are important, closely related coccidian parasites infecting a broad spectrum of hosts and host cells. Infections underly a complex immunological regulation; however, little is known on innate immune reactions to these parasites. To investigate interactions between infected cells and polymorphonuclear neutrophil cells (PMN), PMN adhesion to tachyzoite-infected bovine umbilical vein endothelial cells (BUVECs) under physiological flow conditions and adhesion molecule (E-selectin, P-selectin, VCAM-1, ICAM-1) gene transcription in infected BUVECs were examined in vitro for 72h post-infection (p.i.). BUVECs were rapidly invaded by T. gondii and N. caninum; in general 10-15% of the cells became infected. Tachyzoites were released from 24 and 48h p.i. onwards, for T. gondii and N. caninum, respectively. PMN adhesion to infected cell layers increased early (4h) after infection with both parasites, reached maximum levels 16-24h p.i., but remained enhanced throughout the observation period. PMN adhered to both, infected and non-infected cells within one cell layer, suggesting parasites induced paracrine activation of the BUVECs. Semiquantitative Realtime RT-PCR showed upregulated transcription of the E- and P-selectin genes in BUVECs within 1h p.i. and of ICAM-1 and VCAM-1 genes within 2h p.i. Maximum transcript levels were observed at 4-6h p.i.; the 24h p.i. gene transcription had declined to control levels. In general, T. gondii more strongly induced PMN adhesion and adhesion molecule gene transcription than N. caninum. The data suggest an effective role of PMN in innate immune reactions to these parasites.

The effect of Toxoplasma gondii infection on expression of chemokines by rat retinal vascular endothelial cells

Cells infected by Toxoplasma gondii undergo up-regulation of proinflammatory cytokines, organelle redistribution, and protection from apoptosis. During infection in man, the parasite encysts within the retina, a process that results in retinochoroiditis which can lead to permanent loss of sight. The reasons for the parasite to infect retinal tissue and the mechanisms by which it encysts are not clearly understood. We studied the effect of infection with T. gondii of retinal vascular endothelial cells using the Clontech Atlastrade mark array system in order to elucidate changes in gene expression. We compared hybridization of RNA to the array from infected and uninfected cells at two time points; 2 and 24 h. Exposure to T. gondii after 2 h resulted in change of expression of approximately 6% of genes on the array, including those involved in cell structure, protein and vesicle trafficking, cell-cycle regulation, transcriptional and translational machinery, and apoptosis. Among the genes involved in the inflammatory response, chemokine genes such as GRO1 (Growth Regulated Oncogene 1), MCP-1 (Monocyte Chemotactic Protein-1), FKN (Fractalkine) and RANTES (Regulated upon Activation, Normal T Cell Expressed and Secreted) were found to be up-regulated and protein production was confirmed by ELISA. However after 24 h of infection, GRO1, MCP-1 and FKN were down-regulated, confirmed by RT-PCR. Thus, invasion of retinal vascular endothelium (RVE) cells by T. gondii leads to the production of chemokines important in directing the traffic of inflammatory cells to the infected area.

IMMUNOPATHOLOGIC EFFECTS ASSOCIATED WITH SARCOCYSTIS NEURONA–INFECTED INTERFERON-GAMMA KNOCKOUT MICE

Interferon-gamma knockout (IFN-gamma KO) mice were infected with Sarcocystis neurona merozoites to characterize the immunopathology associated with infection. By day 14 postinfection (PI), mice developed splenomegaly and lymphadenopathy, characterized by marked lymphoid hyperplasia with increased numbers of germinal centers. Additional histopathologic changes included increased extramedullary hematopoiesis, multifocal mixed inflammatory infiltrates in the liver, perivascular infiltrate of the liver and lung, and interstitial pneumonia. The total number of B-cell splenocytes (P < 0.05) and the percentage of B-cells increased on day 14 PI in the spleen and on day 28 PI in the lymph nodes (P < 0.05). By day 28 PI, the number of B-cell splenocytes decreased significantly. A non-subset-specific decrease in percentages of CD4 lymphocytes throughout all lymphoid organs was observed on day 14 PI. However, total CD4 and CD44/CD4 splenocytes increased significantly by day 28 PI. Early-activation CD8 lymphocytes were reduced in the blood and spleen, whereas memory CD8 lymphocyte percentages and total numbers were significantly increased. On the basis of the results, we propose that S. neurona-infected IFN-gamma KO mice are immunocompromised and unable to clear the infection. Thus, they develop B-cell exhaustion and a delayed, but sustained, increased number of memory CD4 and CD8 lymphocytes due to chronic antigen stimulation.

Bax-induced apoptosis not demonstrated in the congenital toxoplasmosis in mice

A prominent neuropathological change observed in a murine model of congenital toxoplasmosis is cerebral cortical hypoplasia. In the early embryonic life of toxoplasmosis mice, the number of apoptotic cell observed in cerebral cortex is increased, indicating that increased number of apoptotic cells might relate to the pathogenetic mechanism of the cortical hypoplasia. Immunohistochemical expression of apoptosis-related factors, Bcl-2 and Bax has been studied in fetal murine brains infected with toxoplasma and in controls. Paraffin sections of the fetal brains on embryonic day (ED) 10, 12, 14, 16 and 18 were applied for the immunostains of Bcl-2 and Bax. Totally, 47 experimental animals (ED10: n=8, ED12: n=6, ED14: n=12, ED16: n=6, ED18: n=15) and 48 control animals (ED10: n=6, ED12: n=8, ED14: n=9, ED16: n=9, ED18: n=16) were examined. Bcl-2 positive cells were detected on ED10, whereas Bax positive cells appeared on ED14. No difference of Bcl-2 and Bax expression between toxoplasmosis and control groups was detected, suggesting that there is no clear relation between Bax-induced apoptosis and cortical dysplasia in congenital toxoplasmosis.